During the combustion process of an internal combustion engine, gasoline is oxidized and hydrogen (H) and carbon (C) combine with air. Various chemical compounds are formed including carbon dioxide (CO2), water (H2O), carbon monoxide (CO), nitrogen oxides (NOx), unburned hydrocarbons (HC), sulfur oxides (SOx), and other compounds.
An exhaust system of the vehicle includes a catalytic converter that reduces CO, HC and NOx in the exhaust gas. The efficiency of the catalytic converter is periodically monitored to prevent excess CO, HC and NOx in the exhaust gas. Typically, the catalytic converter is monitored during steady state engine operation. At idle, for example, the engine controller adjusts the air to fuel (A/F) ratio to achieve consistent emissions output. Traditional monitoring methods force the A/F ratio to a lean or rich condition for a predetermined period. Afterwards, the controller switches to rich or lean conditions. The controller estimates an oxygen storage capacity (OSC) of the catalytic converter based on a lag time between an inlet oxygen sensor and an outlet oxygen sensor detecting the lean/rich condition. The OSC is indicative of the efficiency of the catalytic converter.
Proper function of the outlet oxygen sensor is required for accurate testing of the catalytic converter. However, because of a lag through the catalytic converter response of the outlet oxygen sensor signal is delayed to that of the inlet oxygen sensor signal. For this reason, it is problematical to detect a faulty outlet oxygen sensor using a passive mode only. Thus, a second intrusive diagnostic is traditionally required to confirm proper function of the outlet oxygen sensor. The intrusive tests adversely impact engine stability and exhaust emission levels, eliminate effective closed-loop control, decrease long and short term learning, and disable operation of other vehicle diagnostics. For this reason, minimizing an intrusive time is beneficial for engine operation.